Free up the assignment name after deleting an assignment

Description

Previously, when deleting an assignment, it would hold that name reserved forever. That doesn't happen now. Closes #109 (closed)

Changes

• Free up the assignment name when an assignment is deleted

Test and Review

To be filled in by the reviewers

• All of the methods are commented to expectation

• The methods are tested to satisfaction

• There are no unnecessary files present in the MR

• The continuous integration has no problems with the MR

• The MR is filled in as requested (including labels, milestones, and reviewers)

• The documentation is up-to-date

• All nullable parameters are marked as such

core/src/main/java/nl/tudelft/ewi/auta/core/model/Assignment.java

 package nl.tudelft.ewi.auta.core.model;
 
+import java.time.ZonedDateTime;
 import java.util.Map;
 
 import org.springframework.data.annotation.Id;
@@ -189,6 +190,12 @@ public class Assignment {
      * @param deleted {@code true} if the assignment was deleted, {@code false} otherwise
      */
     public void setDeleted(final boolean deleted) {
+        if (deleted) {
+            final var date = ZonedDateTime.now();
+            this.name = this.name + " (deleted on " + date + ")";
+        } else if (this.name.contains(" (deleted on ")) {
+            this.name = this.name.substring(0, this.name.lastIndexOf(" (deleted on "));
+        }
         this.deleted = deleted;
     }